Evaluating therapeutic stimulation electrode configurations based on physiological responses

ABSTRACT

A medical system comprises a plurality of electrodes; at least one sensor configured to output at least one signal based on at least one physiological parameter of a patient; and a processor. The processor is configured to control delivery of stimulation to the patient using a plurality of electrode configurations. Each of the electrode configurations comprises at least one of the plurality of electrodes. For each of the electrode configurations, the processor is configured to determine a first response of target tissue to the stimulation based on the signals, and a second response of non-target tissue to the stimulation based on the signals. The processor is also configured to select at least one of the electrode configurations for delivery of stimulation to the patient based on the first and second responses for the electrode configurations. As examples, the target tissue may be a left ventricle or vagus nerve.

This application claims the benefit of U.S. Provisional Application No.60/956,832, filed Aug. 20, 2007, U.S. Provisional Application No.60/956,868, filed Aug. 20, 2007 and U.S. Provisional Application No.61/049,245, filed Apr. 30, 3008 each of which are hereby incorporated byreference.

TECHNICAL FIELD

The present disclosure relates to medical devices, more particularly toprogramming a medical device to deliver therapy.

BACKGROUND

In the medical field, a wide variety of medical devices use implantableleads. For example, implantable cardiac pacemakers provide therapeuticstimulation to the heart by delivering pacing, cardioversion, ordefibrillation pulses via implantable leads. Implantable cardiacpacemakers deliver such pulses to the heart via electrodes disposed onthe leads, e.g., near distal ends of the leads. Implantable medicalleads may be configured to allow electrodes to be positioned at desiredcardiac locations so that the pacemaker can deliver pulses to thedesired locations.

Implantable medical leads are also used with other types of stimulatorsto provide, as examples, neurostimulation, muscular stimulation, orgastric stimulation to target patient tissue locations via electrodes onthe leads and located within or proximate to the target tissue. As oneexample, at least one implantable medical lead may be positionedproximate to the vagus nerve for delivery of neurostimulation to thevagus nerve. Additionally, implantable medical leads may be used bymedical devices for patient sensing and, in some cases, for both sensingand stimulation. For example, electrodes on implantable medical leadsmay detect electrical signals within a patient, such as anelectrocardiogram, in addition to delivering electrical stimulation.

For delivery of cardiac pacing pulses to the left ventricle (LV), animplantable medical lead is typically placed through the coronary sinusand into a coronary vein. However, when located in the coronary sinus ora coronary vein, an LV lead may also be located near the phrenic nerve.Phrenic nerve stimulation is generally undesirable during LV pacingtherapy. In some instances, the implantable lead may need to bespecifically positioned to avoid phrenic nerve stimulation during LVpacing therapy, which may result in placing the electrodes of the LVlead at a non-optimal site for LV pacing.

In some cases, implantable medical leads with ring electrodes are usedas an alternative to cuff electrodes for delivery of neurostimulation tothe vagus nerve. However, when located near the vagus nerve, theimplantable medical lead may also be located near neck muscles.Stimulation of neck muscles is generally undesirable during therapeuticvagal neurostimulation.

SUMMARY OF THE DISCLOSURE

Implantable medical leads including a plurality of electrodes mayprovide stimulation therapy using a multitude of electrodeconfigurations. For example, individual electrodes can be configured asanodes or cathodes and any combination of anode and cathode electrodesmay be used. In addition, any of the electrodes may be used as unipolarelectrodes. As another example, a housing of an implantable medicaldevice may also be selected as an anode or cathode in combination withany selected electrode configuration. Different electrode configurationsmay direct stimulation fields to different locations such as differenttissues within a patient.

For any given patient and stimulation therapy, determining at least onepreferred electrode configuration may require a significant amount oftrial and error to determine the efficacy a plurality of potentialelectrode configuration. In addition, for a given set of electrodes,determining a patient's physiological responses can be difficult. Thetechniques disclosed herein may be useful to simplify the selection atleast one preferred electrode configuration and determination of apatient's physiological responses to stimulation therapy includingphysiological response(s) to stimulation therapy resulting from astimulation field interaction with target tissue and non-target tissueof a patient.

A physiological response(s) associated with stimulation fieldinteraction with target tissue may be evaluated according to desiredpatient response(s) to the stimulation therapy, e.g., the effectivenessor efficacy of the stimulation therapy for an electrode configurationincluding current and/or voltage amplitudes for the electrodes includedin the electrode configuration. Similarly, a physiological response(s)associated with stimulation field interaction with non-target tissue maybe evaluated according to unbeneficial patient response(s) to thestimulation therapy, e.g., unwanted side-effect(s) attributable to thestimulation therapy. The physiological response(s) associated withstimulation field interactions with target tissue and non-target tissuefor multiple electrode configurations may be objectively compared todetermine preferable electrode configurations or even a most preferredelectrode configuration for continued stimulation therapy. Examples ofphysiological response(s) include generally desired changes of thefunction of the heart, such as changes in contractility of a heart,cardiac output, electrocardiogram (ECG) morphology, heart rate,intercardiac pressure and a time derivative of intercardiac pressure(dP/dt).

One example of a physiological response is a capture threshold thatproduces a desired patient response to the stimulation therapy. Asreferred to herein, a capture threshold refers to a therapy parameterused in the therapy directed to the target tissue. As examples, thetarget tissue may be a left ventricle or vagus nerve of a patient. Forexample, a capture threshold may be a stimulation voltage amplitude,stimulation current amplitude, stimulation waveform, stimulation pulsewidth, stimulation pulse frequency, other therapy parameter or acombination of therapy parameters that produces desired patientresponse(s) to the stimulation therapy.

In one example, the disclosure provides a medical system comprising aplurality of electrodes; at least one sensor configured to output atleast one signal based on at least one physiological parameter of apatient; and a processor. The processor is configured to controldelivery of stimulation to the patient using a plurality of electrodeconfigurations. Each of the electrode configurations comprises at leastone of the plurality of electrodes. For each of the electrodeconfigurations, the processor is also configured to determine a firstresponse of target tissue to the stimulation based on the signals, and asecond response of non-target tissue to the stimulation based on thesignals. The processor is also configured to select at least one of theelectrode configurations for delivery of stimulation to the patientbased on the first and second responses for the electrodeconfigurations.

In another example, the disclosure provides a method for evaluatingtherapeutic stimulation of a plurality of electrode configurationscomprising controlling delivery of stimulation to a patient using theplurality of electrode configurations; for each of the electrodeconfigurations, determining a first response of target tissue to thestimulation and a second response of non-target tissue to thestimulation based on at least one sensor signal, wherein the sensorsignals are based on at least one physiological parameter of thepatient; and selecting at least one of the electrode configurations fordelivery of stimulation to the patient based on the first and secondresponses for the electrode configurations.

In an example, the disclosure provides a computer-readable mediumcomprising instructions that cause a programmable processor to controldelivery of stimulation to a patient using a plurality of electrodeconfigurations; for each of the electrode configurations, determine afirst response of target tissue to the stimulation and a second responseof non-target tissue to the stimulation based on at least one sensorsignal, wherein the sensor signals are based on at least onephysiological parameter of the patient; and select at least one of theelectrode configurations for delivery of stimulation to the patientbased on the first and second responses for the electrodeconfigurations.

In another example, the disclosure provides a medical device comprisinga means for delivering stimulation therapy to a patient using aplurality of electrode configurations; and a means for evaluating therelative suitability of the of the electrode configurations fordelivering stimulation therapy to target tissue of the patient.

The details of the present disclosure are set forth in the accompanyingdrawings and the description below. Other features, objects, andbenefits of the present disclosure will be apparent from the descriptionand drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating an example implantablemedical device system.

FIG. 2 is a functional block diagram of an example embodiment of theimplantable medical device (IMD) of FIG. 1.

FIG. 3 is a functional block diagram of an example embodiment of theexternal programmer of FIG. 1.

FIG. 4A is a side view of a distal end of an example lead includingelectrode segments at its distal tip.

FIGS. 4B-4D are cross-sectional views of the electrode segments at thedistal tip the lead of FIG. 4A and an electrical field propagatingdirectionally from the electrode segments.

FIG. 5A is a side view of a distal end of another example lead includingelectrode segments at its distal tip.

FIG. 5B is a cross-sectional view of the electrode segments at thedistal tip the lead of FIG. 5A

FIG. 6 is a side view of a distal end of an example lead including arecessed electrode.

FIG. 7 is a side view of a distal end of an example lead including aprotruded electrode.

FIG. 8 is a side view of a distal end of another example lead includingelectrode segments at its distal end.

FIG. 9 is a flow diagram illustrating an example technique forevaluating at least one electrode configuration of an implantablemedical lead for left ventricle (LV) pacing in a patient.

FIG. 10 is a flow diagram illustrating an example technique forevaluating a plurality of electrode configurations for LV pacing in apatient.

FIG. 11 is a side view of a distal end of an example lead including twopairs of closely spaced electrodes.

DETAILED DESCRIPTION

While the description primarily refers to implantable electricalstimulation leads and implantable medical devices that deliverstimulation therapy to a patient's heart, e.g., pacemakers, andpacemaker-cardioverter-defibrillators, the features and techniquesdescribed herein are useful in other types of medical device systems,which may include other types of implantable medical leads andimplantable medical devices. For example, the features and techniquesdescribed herein may be used in systems with medical devices thatdeliver neurostimulation to the vagal nerve. As other examples, thefeatures and techniques described herein may be embodied in systems thatdeliver other types of neurostimulation therapy (e.g., spinal cordstimulation or deep brain stimulation), stimulation of at least onemuscle or muscle groups, stimulation of at least one organ such asgastric system stimulation, stimulation concomitant to gene therapy,and, in general, stimulation of any tissue of a patient.

In addition, while the examples shown in the figures include leadscoupled at their proximal ends to a stimulation therapy controller,e.g., implantable medical device, located remotely from the electrodes,other configurations are also possible and contemplated. In someexamples, a lead comprises a portion of a housing, or a member coupledto a housing, of stimulation generator located proximate to or at thestimulation site, e.g., a microstimulator. In other examples, a leadcomprises a member at stimulation site that is wirelessly coupled to animplanted or external stimulation controller or generator. For thisreason, as referred to herein, the term of a “lead” includes anystructure having at least one stimulation electrode disposed on itssurface.

FIG. 1 is a conceptual diagram illustrating an example implantablemedical system 10 comprising an implantable medical device (IMD) 12, andimplantable medical leads 14, 16 electrically coupled to IMD 12. In theembodiment shown in FIG. 1, system 10 is implanted within a patient 18to deliver electrical stimulation therapy to the heart 5 of patient 18.Patient 18 ordinarily, but not necessarily, will be a human patient.

In the embodiment shown in FIG. 1, IMD 12 is a cardiac pacemaker,cardioverter, defibrillator, or pacemaker-cardioverter-defibrillator(PCD) that generates therapeutic electrical stimulation for pacing,cardioversion or defibrillation, which may take the form of pulses orcontinuous time signals. Leads 14, 16 each include at least oneelectrode that are each positioned within (e.g., intravenously) orproximate to (e.g., epicardially) heart 5 in order to deliver thetherapeutic electrical stimulation from IMD 12 to heart 5. In someembodiments, at least one of leads 14, 16 may provide stimulation toheart 5 without contacting heart 5, e.g., at least one of leads 14, 16may include a subcutaneous electrode.

In the illustrated embodiment, a distal end of lead 14 is positionedproximate to the left ventricle (LV) of patient 18 and, moreparticularly, within the coronary sinus or a coronary vein accessed viathe coronary sinus. In the illustrated embodiment, lead 14 is configuredfor intravenous introduction into heart 5. For example, lead 14 may havea lead body diameter of between 0.020 inches and 0.100 inches. A distalend of lead 16 is positioned within the right ventricle of patient 18.Accordingly, in the illustrated example, lead 14 may be referred to as aleft ventricular (LV) lead, and lead 16 may be referred to as a rightventricular (RV) lead. IMD 12 may deliver coordinated pacing signals toheart 5 via leads 14 and 16 to, for example, to resynchronize the actionof the left and right ventricles.

When lead 14 is positioned within the coronary sinus or a coronary vein,lead 14 may be proximate to the phrenic nerve. This positioning mayresult in unintentional phrenic nerve stimulation, which is generallyundesirable during LV pacing therapy. For example, phrenic nervestimulation may cause a hiccup each time a stimulation signal isdelivered to stimulate LV contraction, e.g., with each heart beat. Itmay be desirable to selectively stimulate the myocardium of the LV ofheart 5 without stimulating the phrenic nerve. Accordingly, as describedin further detail below, at least one electrode configuration of lead 14may be evaluated to assess physiological response(s) associated withstimulation field interaction with a patient's myocardial and phrenicnerves. Evaluation of physiological response(s) associated withstimulation field interaction with a patient's myocardial and phrenicnerves may help guide selection of an electrode configuration thatselectively stimulates the LV without stimulating the phrenic nerve.

As another example, lead 14 may be positioned within the internaljugular vein for vagus nerve stimulation. Consequently, lead 14 may bepositioned proximate to the neck muscles of patient 18. Stimulation ofthe muscle tissue of the neck may cause undesirable muscle contraction.Therefore, it may be desirable to selectively stimulate the vagus nervewithout stimulating the muscle tissue proximate to the vagus nerve. Atleast one electrode configuration of lead 14 may be evaluated to assessphysiological response(s) associated with stimulation field interactionwith a patient's vagus nerve and neck muscles. Evaluation ofphysiological response(s) associated with stimulation field interactionwith a patient's vagus nerve and neck muscles may help guide selectionof an electrode configuration that selectively stimulates the vagusnerve without stimulating the neck muscles.

As previously mentioned, leads including the features described hereinmay be used to deliver neurostimulation therapy from a medical device totarget neural tissues of a patient, such as the vagal nerve.Furthermore, although described herein as being coupled to IMDs,implantable medical leads may also be percutaneously coupled to anexternal medical device for deliver of electrical stimulation to targetlocations within the patient.

As shown in FIG. 1, system 10 may also include a programmer 19, whichmay be a handheld device, portable computer, or workstation thatprovides a user interface to a clinician or other user. The clinicianmay interact with the user interface to program stimulation parametersfor IMD 12, which may include, for example, the electrodes of leads 14,16 that are activated, the polarity of each of the activated electrodes,a current or voltage amplitude for each of the activated electrodes and,in the case of stimulation in the form of electrical pulses, pulse widthand pulse rate (or frequency) for stimulation signals to be delivered topatient 18. As referred to herein, an amplitude of stimulation therapymay be characterized as a magnitude of a time varying waveform. Forexample, an amplitude of stimulation therapy may be measured in terms ofvoltage (volts), current (ampere), or electric field (volts/meter).Typically, amplitude is expressed in terms of a peak, peak to peak, orroot mean squared (rms) value. The clinician may also interact with theuser interface to program escape intervals, rate response parameters, orany other stimulation parameters known for use in controlling cardiacpacing, or other types of therapeutic stimulation.

Programmer 19 supports telemetry (e.g., radio frequency telemetry) withIMD 12 to download stimulation parameters and, optionally, uploadoperational or physiological data stored by IMD 12. In this manner, theclinician may periodically interrogate IMD 12 to evaluate efficacy and,if necessary, modify the stimulation parameters. IMD 12 and programmer19 may communicate via cables or a wireless communication, as shown inFIG. 1. Programmer 19 may, for example, communicate via wirelesscommunication with IMD 12 using RF telemetry techniques known in theart.

In some embodiments, at least one of the electrodes of leads 14, 16, orone or more different leads, may include at least one sense electrode orsensor that senses a physiological parameter of patient 12, such as, butnot limited to, electrocardiogram (ECG) parameters, a heart rate, QRSwidth, atrioventricular (AV) Dissociation, respiration rate, respiratoryvolume, core temperature, diaphragmatic stimulation such as hiccups,skeletal muscle activity, blood oxygen level, cardiac output, bloodpressure, intercardiac pressure, time derivative of intercardiacpressure (dP/dt), electromyogram (EMG) parameters, orelectroencephalogram (EEG) parameters. Sense electrodes may be the sameelectrodes used for delivery of electrical stimulation to patient 18, ordifferent electrodes. Therapy system 10 may also include at least onesensor 17 in addition to or instead of sense electrodes and sensors onthe leads 14, 16. Sensor 17 may be configured to detect an activitylevel, motion, posture, intracardiac, intravascular or other pressurewithin the patient, or another physiological parameter of patient 18.For example, sensor 17 may comprise an accelerometer. Sensor 17 maygenerate a signal that varies as a function of at least onephysiological parameter of patient 18.

Sensor 17 may be implanted within or external to patient 18, and may bewirelessly coupled to IMD 12 or coupled to IMD 12 via a lead, such asleads 14, 16 or another lead. For example, sensor 17 may be implantedwithin patient 18 at a different site than IMD 12 or sensor 17 may beexternal. As one example sensor 17 may include an accelerometer usefulto detect, e.g., the presence of cardiac pulse, diaphragmaticstimulation such as hiccups and/or skeletal muscle activity. In someexamples, sensor 17 may be located on or within a housing of IMD 12. Inaddition or instead of being coupled to IMD 12, in some cases, sensor 17may be wirelessly coupled to programmer 19 or coupled to programmer 19by a wired connection. As used herein, the term “sensor” refers to atleast one electrode, or any other sensor, that provides a signal thatvaries as a function of a sensed physiological parameter.

FIG. 2 is a functional block diagram of IMD 12 according to one example.In the example illustrated in FIG. 2, IMD 12 includes processor 20,memory 22, power source 24, communication module 26, signal generator28, and switch device 29. As shown in FIG. 2, switch device 29 iscoupled to leads 14 and 16. Alternatively, switch device 29 may becoupled to more than two leads directly or indirectly (e.g., via a leadextension, such as a bifurcating lead extension that may electricallyand mechanically coupled to two leads) as needed to provide stimulationtherapy to patient 18.

Memory 22 includes computer-readable instructions that, when executed byprocessor 20, cause IMD 12 and processor 20 to perform various functionsattributed to IMD 12 and processor 20 herein. Memory 22 may include anyvolatile, non-volatile, magnetic, optical, or electrical media, such asa random access memory (RAM), read-only memory (ROM), non-volatile RAM(NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory,or any other digital media.

Stimulation generator 28 produces stimulation signals (e.g., pulses orcontinuous time signals, such as sine waves) for delivery to patient 18via selected combinations of electrodes carried by leads 14, 16.Processor 20 controls stimulation generator 28 to apply particularstimulation parameters specified by at least one of programs (e.g.,programs stored within memory 22), such as amplitude, pulse width, andpulse rate. Processor 20 may include a microprocessor, a controller, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field-programmable gate array (FPGA), equivalentdiscrete or integrated logic circuitry, or any combination of at leastone these elements.

Processor 20 also controls switch device 29 to apply the stimulationsignals generated by stimulation generator 28 to selected combinationsof the electrodes of leads 14, 16 with a polarity, e.g., as specified byat least one stimulation programs or parameters stored in memory 22and/or received from programmer 19 via communication module 26. Inparticular, switch device 29 couples stimulation signals generated bystimulation generator 28 to selected conductors within leads 14, 16which, in turn, delivers the stimulation signals across selectedelectrodes of leads 14, 16. Switch device 29 may be a switch array,switch matrix, multiplexer, or any other type of switching devicesuitable to selectively couple stimulation energy to selectedelectrodes. Hence, stimulation generator 28 is coupled to the electrodesof leads 14, 16 via switch device 29 and conductors within leads 14, 16.

Stimulation generator 28 may be a single- or multi-channel stimulationgenerator. In particular, stimulation generator 28 may be capable ofdelivering, a single stimulation pulse, multiple stimulation pulses, ora continuous signal at a given time via a single electrode combinationor multiple stimulation pulses at a given time via multiple electrodecombinations. In some embodiments, multiple channels of stimulationgenerator 28 may provide different stimulation signals, e.g., pulses, todifferent electrodes at substantially the same time. For example,multiple channels of stimulation generator 28 may provide signals withdifferent amplitudes to different electrodes at substantially the sametime. Processor 20 may control stimulation generator 28 to generatestimulation in accordance with at least one programs or parametersstored in memory 22 and/or received from programmer 19 via communicationmodule 26. In the case of electrical stimulation pulses, the programs orparameters may specify amplitude, width and rate for pulses generated bystimulation generator 28.

Communication module 26 supports wireless communication between IMD 12and an external programmer 19 or another computing device under thecontrol of processor 20. In some embodiments, communication module 26may include a transmitter and receiver to permit bi-directionalcommunication between IMD 12 and programmer 19. Processor 20 of IMD 14may receive, as updates to programs, values for various stimulationparameters such as amplitude and electrode combination, from programmer19. The updates to the therapy programs may be stored within memory 22.Additionally, processor 20 may send status and operational informationto programmer 19 via communication module 26.

The various components of IMD 12 are coupled to power source 24, whichmay include a rechargeable or non-rechargeable battery. Anon-rechargeable battery may be selected to last for several years,while a rechargeable battery may be inductively charged from an externaldevice, e.g., on a daily or weekly basis. In other embodiments, powersource 24 may be powered by proximal inductive interaction with anexternal power supply carried by patient 18.

Processor 20 may also receive physiological signals sensed by selectedelectrodes on leads 14, 16 or other leads via switch device 29. In someexamples, processor 20 may receive physiological signals sensed by atleast one electrode (not shown) located on housing 13 (FIG. 1) of IMD12, which may be used alone or in combination with lead-borne electrodesfor delivery of stimulation or sensing. Furthermore, processor 20 mayadditionally or alternatively receive at least one signal generated byone or more other sensors 17 that are on or within housing 13, orcoupled to processor 20 via a lead or wirelessly, e.g. via communicationmodule 26.

Such physiological signals may include sensing an evoked R-wave orP-wave after delivery of pacing therapy, sensing for the absence of anintrinsic R-wave or P-wave prior to delivering pacing therapy, ordetecting a conducted depolarization in an adjacent heart chamber. Aswith stimulation therapy, selecting which electrode(s) are used forsensing physiological parameters of a patient may alter the signalquality of the sensing techniques. For this reason, sensing techniquesmay include one or more algorithms to determine the suitability of eachelectrode or electrode combination in the stimulation therapy system forsensing at least one physiological parameter. Sensing physiologicalparameters may also be accomplished using electrode or sensors that areseparate from the stimulation electrodes, e.g., electrodes capable ofdelivering stimulation therapy, but not selected to deliver thestimulation therapy that is actually being delivered to the patient.

FIG. 3 is a functional block diagram of an example embodiment ofexternal programmer 19. As shown in FIG. 3, external programmer 19includes processor 40, memory 42, user interface 44, communicationmodule 46, and power source 48. A clinician or another user may interactwith programmer 19 to generate and/or select therapy programs fordelivery by IMD 12. For example, in some embodiments, programmer 19 mayallow a clinician to define stimulation fields, e.g., select appropriatestimulation parameters for one or more stimulation programs to definethe desired stimulation field. Programmer 19 may be used to selectstimulation programs, generate new stimulation programs, and transmitthe new programs to IMD 12. Processor 40 may store stimulationparameters as one or more stimulation programs in memory 42. Processor40 may send programs to IMD 12 via communication module 46 to controlstimulation automatically and/or as directed by the user.

Programmer 19 may be one of a clinician programmer or a patientprogrammer, i.e., the programmer may be configured for use depending onthe intended user. A clinician programmer may include more functionalitythan the patient programmer. For example, a clinician programmer mayinclude a more featured user interface, allow a clinician to downloadtherapy usage, sensor, and status information from IMD 12, and allow aclinician to control aspects of IMD 12 not accessible by a patientprogrammer embodiment of programmer 19.

A user, e.g., a clinician or patient 18, may interact with processor 40through user interface 44. User interface 44 may include a display, suchas a liquid crystal display (LCD), light-emitting diode (LED) display,or other screen, to show information related to stimulation therapy, andbuttons or a pad to provide input to programmer 19. Buttons may includean on/off switch, plus and minus buttons to zoom in or out or navigatethrough options, a select button to pick or store an input, and pointingdevice, e.g. a mouse, trackball, or stylus. Other input devices may be awheel to scroll through options or a touch pad to move a pointing deviceon the display. In some embodiments, the display may be a touch screenthat enables the user to select options directly from the displayscreen.

Programmer 19 may be a handheld computing device, a workstation oranother dedicated or multifunction computing device. For example,programmer 19 may be a general purpose computing device (e.g., apersonal computer, personal digital assistant (PDA), cell phone, and soforth) or may be a computing device dedicated to programming IMD 12.

Processor 40 processes instructions from memory 42 and may store userinput received through user interface 44 into the memory whenappropriate for the current therapy. Processor 40 may comprise any atleast one of a microprocessor, digital signal processor (DSP),application specific integrated circuit (ASIC), field-programmable gatearray (FPGA), or other digital logic circuitry.

Memory 42 may include instructions for operating user interface 44,telemetry module 46, and managing power source 48. Memory 42 may storeprogram instructions that, when executed by processor 40, cause theprocessor and programmer 19 to provide the functionality ascribed tothem herein. Memory 42 may include any at least one of a random accessmemory (RAM), read-only memory (ROM), electronically-erasableprogrammable ROM (EEPROM), flash memory, or the like.

Wireless communication in programmer 19, IMD 12 and sensors 17 may beaccomplished by radio frequency (RF) communication or proximal inductiveinteraction of between such devices. This wireless communication ispossible in programmer 19 through the use of communication module 46.Accordingly, communication module 46 may include any circuitry known forsuch communication. For example, communication module 46 may include atransmitter and receiver to permit bi-directional communication betweenprogrammer 19 and IMD 12.

Power source 48 delivers operating power to the components of programmer19. Power source 48 may include a battery and a power generation circuitto produce the operating power. In some embodiments, the battery may berechargeable to allow extended operation. Recharging may be accomplishedthrough proximal inductive interaction, or electrical contact withcircuitry of a base or recharging station. In other embodiments, primarybatteries may be used. In addition, programmer 19 may be directlycoupled to an alternating current source, such would be the case withsome computing devices, such as personal computers.

FIGS. 4-8 illustrate various embodiments of implantable medical leadsthat may be utilized to deliver, as examples, LV or vagus nervestimulation. As described in further detail with respect to FIGS. 9 and10, at least one electrode configuration of one or more of the leads ofFIGS. 4-8 may be evaluated to assess myocardial and phrenic nervecapture for LV pacing, or vagus nerve and neck muscle capture for vagusnerve stimulation. Evaluation of myocardial and phrenic nerve capturemay help guide selection of an electrode configuration that selectivelystimulates the LV without stimulating the phrenic nerve. Similarly,evaluation of vagus nerve and neck muscle capture may help guideselection of an electrode configuration that selectively stimulates thevagus nerve without stimulating the neck muscles.

FIG. 4A is a side view of a distal end of an embodiment of a lead 50,which may, for example, correspond to either of leads 14, 16 of FIG. 1.A proximal end (not shown) of lead 50 may be coupled to an IMD (e.g.,IMD 12 of FIG. 1). Lead 50 includes a lead body 52 and electrodes 54A,54B, and 56A-56D (electrodes 56C and 56D are not shown in FIG. 4A). Leadbody 52 may be formed from a insulative biocompatible material.Exemplary biocompatible material includes at least one covers ofpolyurethane, silicone, and fluoropolymers such as tetrafluroethylene(ETFE), polytetrafluroethylene (PTFE), and/or expanded PTFE (i.e. porousePTFE, nonporous ePTFE). Electrodes 54A, 54B, and 56A-56D are exposed totissue of the patient, which allows data to be sensed from the tissueand/or therapy delivered to the patient.

As shown in FIG. 4A, electrodes 54A and 54B are flush or isodiametricwith lead body 22 and may be segmented or partial ring electrodes, eachof the electrode segments 54A and 54B extending along an arc less than360 degrees (e.g., 90-120 degrees). Segmented or partial ring electrodesmay be useful for providing an electrical stimulation field that ispredominantly focused in a particular transverse direction relative tothe longitudinal axis of lead 50, and/or targeting a particularstimulation site. In other embodiments, instead of or in addition toelectrodes 54A and 54B, lead 50 may include a ring electrode extendingsubstantially around the entire periphery, e.g., circumference, of lead50.

In the illustrated embodiment, electrodes 56A-56D are also segmented orpartial ring electrodes, which do not extend substantially around theentire periphery of the lead body 52. Electrodes 56C and 56D are locatedon the circumferential portion of lead body 52 not visible in FIG. 4A.As described in further detail below, FIG. 4B is a cross-sectional viewof electrodes 56A-56D along line 4B in FIG. 4A, and illustrates theapproximate locations of electrodes 56C and 56D. Electrodes 56A-56D may,but need not be, located at the same axial position along the length oflead body 52. When electrodes 56A-56D are located at the same axialposition of lead body 52, electrodes 56A-56D may form a row of electrodesegments. In some embodiments, electrodes 56A-56D may be evenly spacedaround the periphery of lead 50. Additionally, each of individualelectrode segments 56A-56D may be separated by insulative material 58,which may aid in electrically isolating each of electrodes 56A-56D.

Each of electrodes 54A, 54B, and 56A-56D can be made from anelectrically conductive, biocompatible material, such as platinumiridium. In addition, at least one of electrodes 54A, 54B, and 56A-56Dmay function as sensing electrodes that monitor internal, physiological,electrical signals of patient 18 (FIG. 1). The configuration, type, andnumber of electrodes 54A, 54B, and 56A-56D are merely exemplary. Inother embodiments, lead 50 may include any configuration, type, andnumber of electrodes 54A, 54B, and 56A-56D, and is not limited to theembodiment illustrated in FIGS. 4A and 4B.

Within lead body 52, lead 50 also includes insulated electricalconductors 60A and 60B coupled to electrodes 54A and 54B, and insulatedelectrical conductors 62A-62D coupled to electrode segments 56A-56D,respectively. In the illustrated embodiment, conductors 62A-62D arecoiled along the length of lead body 52 (e.g., in a multiconductorcoil), and conductors 60A and 60B lie axial to conductors 62A-62D.Conductors 60A and 60 B may or may not be coiled. In the embodimentillustrated in FIG. 4A, each of conductors 60A, 60B, and 62A-62D iselectrically coupled to a single one of electrodes 54A, 54B, and56A-56D, respectively. In this manner, each of electrodes 54A, 54B, and56A-56D may be independently activated. In other embodiments, a leadincluding multiple electrodes may include a multiplexer or otherswitching device such that the lead may include fewer conductors thanelectrodes, while allowing each of the electrodes to be independentlyactivated. The switching device may be responsive to commands from theIMD or an external source to selectively couple the electrodes to theconductors for delivery of stimulation or for sensing.

The configuration, type, and number of conductors 60A, 60B, and 62A-62Dis not limited to the embodiment illustrated in FIG. 4A and, in otherembodiments, lead 50 may include any configuration, type, and number ofconductors. As one example, in some embodiments, each of conductors 60A,60B, and 62A-62D may be coiled conductors. Additionally oralternatively, one conductor may be electrically coupled to at least twoelectrodes.

FIG. 4B is a cross-sectional view electrode segments 56A-56D along line4B in FIG. 4A. As previously described, each of electrode segments56A-56D is separated by insulative material 58. The center of lead body52 may include a lumen 64 to accommodate a delivery device such as astylet, guidewire or a hybrid of a stylet and guidewire. A deliverydevice may be used to help position lead 50 at a target location duringimplantation of lead 50. Electrical conductors 62A-62D are coupled toelectrode segments 56A-56D, respectively. Each of conductors 62A-62Dextends from electrodes 56A-56D to a proximal end of lead body 52 tocouple electrodes 56A-56D to an IMD (e.g., IMD 12 of FIG. 1).

Electrode segments 56A-56D may be useful in directing a stimulationfield toward a target site and/or away from a non-target, potentiallyundesirable, site. For example, at least one of electrode segments56A-56D may be activated (e.g., as a cathode or an anode) to deliverstimulation to patient 18 (FIG. 1). As will be described in greaterdetail below, the direction of the stimulation field, e.g., the radialdirection relative to the longitudinal axis of elongated lead body 52 or“side” of the lead on which the field is present, may be based on whichof electrode segments 56A-56D are activated. Electrodes 54A and 54B mayfurther aid in steering the stimulation field in a particular directionand/or sensing a patient condition on a particular side of lead body 52Additionally, a current or voltage amplitude may be selected for each ofthe active electrodes. During movement of lead 20, at least one of theelectrodes may produce different amplitudes to further aid incontrolling the direction of the stimulation field. All else equal, in asystem having two anodes with different amplitudes, each anode adjacentto a cathode, generally, the stimulation field is at least partiallybiased towards the anode with the higher current or voltage amplitude.

As one example, a directional stimulation field may be particularlyuseful in LV pacing applications. An IMD (e.g., IMD 12 of FIG. 1) mayconfigure electrodes 54A, 54B, and 56A-56D to direct the stimulationfield toward the myocardium and away from the phrenic nerve. Morespecifically, when lead 50 is transvenously placed proximate to the LVof patient 18 (FIG. 1), it may be desirable to only activate at leastone of electrodes 54A, 54B, and 56A-56D positioned proximate to themyocardium (e.g., facing or in contact with the myocardium) rather thanthose proximate to the epicardium. Selectively activating at least oneof electrodes 54A, 54B, and 56A-56C to direct the electrical stimulationfield towards the myocardium may reduce the amount of energy requiredfor tissue capture of the myocardium for pacing therapies and,consequently, increase battery life. In addition, directing theelectrical stimulation field towards the myocardium may reduce thelikelihood of phrenic nerve stimulation, because the electricalstimulation field will generally be directed away from the phrenicnerve. In other words, when the electrical stimulation field is directedtoward the myocardium, the excess electrical field directed away fromthe myocardium and across the pericardium where the phrenic nerve liesthat may be present when the electrical stimulation is delivered via aring electrode that extends substantially completely around thecircumference or periphery of a lead may be reduced or eliminated.

A directional stimulation field may be particularly useful when phrenicnerve stimulation occurs post-implant. Using a conventional LV lead,when phrenic nerve stimulation occurs post-implant, the clinician mayneed to either extract the lead to reposition it or abandon LV pacing.Using a lead with electrode segments, the clinician may alter theelectrode configuration to aid in directing the stimulation field awayfrom the phrenic nerve.

As another example, a directional stimulation field may be useful instimulation of the vagus nerve. Stimulation of the vagus nerve may beperformed to decrease heart rate. The vagus nerve is positionedproximate to muscles of the neck, which may inadvertently be stimulatedalong with the vagus nerve. Controlling the direction of propagation ofthe stimulation field may aid in preventing stimulation of the neckmuscles. As another example, a directional electrical field may beuseful in atrial stimulation where it may be desirable to avoidstimulating specific ischemic tissue regions which may result in anarrhythmia. In general, electrodes segments 54A, 54B, and 56A-56D may beuseful in any application where controlling the direction of propagationof the stimulation field is desirable.

In one embodiment, the IMD (e.g., IMD 12 of FIG. 1) may configure afirst electrode segment as a cathode and two adjacent electrodesegments, which may be on opposite sides of the first electrode segment,as anodes. This configuration may be referred to as an “anodalshielding” configuration in the sense that the anodes act as a shieldaround the cathode to substantially prevent propagation of theelectrical field from the cathode to tissue that is beyond the anodes,e.g., tissue on an opposite side of the anode than the cathode.

For example, IMD 12 may configure electrode segment 56B as a cathode andadjacent electrodes segments 56A and 56C on opposite sides of electrodesegment 56B as anodes. Electrode segments 56A and 56C (the anodes) maysubstantially constrain the electrical field propagating from electrodesegment 56B (the cathode) to the side or angular section 68 of lead 50that includes electrode segment 56B. The electrical field may becentered between electrode segments 56A and 56C and, depending on thestimulation amplitudes for each of electrode segments 56A-56C, may becentered substantially over electrode segment 56B. IMD 12 may activateelectrode segments 56A-56D in different configurations based on thedesired direction of the stimulation field. At least one of electrodesegments 54A and 54B may additionally or alternatively be activated asan anode or cathode to aid in controlling the direction of propagationof the stimulation field.

Anodal shielding may limit the size of the stimulation field. Forexample, the anodes may determine the extent and shape of a volume oftissue to which the stimulation field propagates. In some embodiments,an anodal shielding configuration may prevent the stimulation field fromextending past the anodes.

The spacing between each of electrode segments 56A-56D may alsoinfluence the size of the stimulation field. In the embodimentillustrated in FIG. 4B, electrodes 56A-56D are evenly or about evenlyspaced around the periphery of lead 50 with arc 66 separating each ofelectrodes 56A-56D. Separation arc 66 may be selected based on thedesired size of the stimulation field. In other embodiments, electrodesegments 56A-56C may be unevenly spaced around the periphery of lead 50.

FIG. 4C is another cross-sectional view of electrode segments 56A-56D.FIG. 4C illustrates stimulation field 67 emanating from lead body 52. Asdescribed with respect to FIG. 4B, IMD 12 may configure electrodesegment 56B as a cathode and adjacent electrodes segments 56A and 56C onopposite sides of electrode segment 56B as anodes. Electrode segments56A and 56C (the anodes) may substantially constrain stimulation field67 from propagating past electrode segments 56A and 56C (the anodes). Inthe embodiment illustrated in FIG. 4C, stimulation field 67 issubstantially centered over electrode segment 56B. For example,substantially similar voltage amplitudes may vary by no more than 0.1volts, and substantially similar current amplitudes may vary by no morethan 0.1 milliamps. IMD 12 may activate each of electrode segments56A-56C with substantially the same amplitude to generate stimulationfield 67 substantially centered over electrode segment 56B. IMD 12 mayactivate electrode segments 56A-56D in different configurations based onthe desired direction of the stimulation field.

FIG. 4D is another cross-sectional view of electrode segments 56A-56D.FIG. 4D illustrates stimulation field 69 emanating from lead body 52. Asdescribed with respect to FIGS. 4B and 4C, IMD 12 may configureelectrode segment 56B as a cathode and adjacent electrodes segments 56Aand 56C on opposite sides of electrode segment 56B as anodes. Electrodesegments 56A and 56C (the anodes) may substantially constrainstimulation field 69 from propagating past electrode segments 56A and56C (the anodes). In the embodiment illustrated in FIG. 4D, stimulationfield 69 is skewed toward electrode 56C compared to stimulation field 67of FIG. 4C. Rather than being substantially centered over electrode 56B(the central cathode), stimulation field 69 is shifted toward electrode56C. IMD 12 may activate electrode segments 56A-56C with differentcurrent or voltage amplitudes to generate stimulation field 69 shiftedtoward electrode 56C. Additionally, IMD 12 may activate electrodesegments 56A-56D in different configurations based on the desireddirection of the stimulation field. For example, IMD 12 may selectivelyactivate two electrode segments 26A-26D a bipolar configuration.

FIG. 5A is a side view of a distal end of another embodiment of a lead70. A proximal end (not shown) of lead 70 may be coupled to an IMD(e.g., IMD 12 of FIG. 1). Lead 70 includes a lead body 72 and electrodes74 and 76A-76C. An outer surface of lead body 72 may be formed from abiocompatible material such as, for example, polyurethane or silicone.As shown in FIG. 5A, electrode 74 may be a ring electrode extendingsubstantially around the entire periphery, e.g., circumference, of lead70. In other embodiments, electrode 74 may comprise segmented or partialring electrodes, each of the electrode segments extending along an arcless than 360 degrees (e.g., 90-120 degrees).

In the illustrated embodiment, electrodes 76A-76C are segmentedelectrodes, which do not extend substantially around the entireperiphery of the lead 70. Electrodes 76A-76C may, but need not be,located at the same axial position along the length of lead body 72.When electrodes 76A-76C are located at the same axial position of leadbody 72, electrodes 76A-76C may form a row of electrode segments. Insome embodiments, electrodes 76A-76C may be evenly spaced around theperiphery of lead 70. Additionally, each of individual electrodesegments 76A-76C may be separated by insulative material 78, which mayaid in electrically isolating each of electrodes 76A-76C. Insulativematerial 48 is a biocompatible material having an impedance sufficientto prevent shorting between electrode segments during stimulationtherapy. For example, insulative material 48 may comprise polyurethane,silicone, and fluoropolymers such as tetrafluroethylene (ETFE),polytetrafluroethylene (PTFE), and/or expanded PTFE (i.e. porous ePTFE,nonporous ePTFE).

Each of electrodes 74 and 76A-76C can be made from an electricallyconductive, biocompatible material, such as platinum iridium. Inaddition, at least one of electrodes 74 and 76A-76C may function assensing electrodes that monitor internal physiological signals ofpatient 18 (FIG. 1). The configuration, type, and number of electrode 74and 76A-76C are merely exemplary. In other embodiments, lead 70 mayinclude any configuration, type, and number of electrodes 74 and 76A-76Cand is not limited to the embodiment illustrated in FIGS. 5A.

Electrode segments 76A-76C may be useful in directing a stimulationfield toward a target site and/or away from a non-target, potentiallyundesirable, site. For example, at least one of electrode segments76A-76C may be activated (e.g., as a cathode or an anode) to deliverstimulation to patient 18 (FIG. 1). The direction of the stimulationfield may be based on which electrode segments 76A-76C are activated. Acurrent or voltage amplitude may be selected for each of the activeelectrodes to further aid in controlling the direction of thestimulation field. Electrodes activated with unequal amplitudes mayshift the direction of the stimulation field relative to a centralposition of a group of active electrodes, e.g., relative to a centralcathode, such as described with respect to stimulation field 69 of FIG.4D. For example, unequal voltage amplitudes may vary by at least 0.1volts, and unequal current amplitudes may vary by at least 0.1milliamps.

An IMD (e.g., IMD 12 of FIG. 1) may configure electrode segments 76A-76Cin an anodal shielding configuration. For example, IMD 12 may configureelectrode segment 76A as a cathode and electrode segments 76B and 76C onopposite sides of electrode segment 76A as anodes. Anodal shielding maylimit the size of the stimulation field. For example, the anodes maydetermine the extent and shape of area that experiences the effect ofthe stimulation field. In some embodiments, an anodal shieldingconfiguration may prevent the stimulation field from extending past theanodes.

Electrode 74 may allow a conventional electrode configuration, which maybe used as an alternative to configurations including electrode segments76A-76C. Conventionally, a LV lead may utilize a ring electrode as acathode and the IMD (e.g., IMD 12 of FIG. 1) or a conductive portion(e.g., a coil electrode) on another lead (e.g., a lead with a distal endimplanted in the right ventricle) as an anode in a unipolarconfiguration. As one example, a superior vena cava (SVC) coil and/or aright ventricle (RV) coil of a lead with a distal end implanted in theright ventricle may be activated as an anode. Electrode 74 may activatedas cathode in a conventional unipolar configuration. Electrode 74 mayprovide a clinician with a familiar fall-back configuration.

Lead 70 also includes electrical conductor 80 coupled to electrode 74,and electrical conductors 82A-82C coupled to electrode segments 76A-76C,respectively. In the illustrated embodiment, conductors 82A-82C arecoiled along the length of lead body 72 (e.g., in a multiconductorcoil), and conductor 80 lies axial to conductors 82A-82C. In theembodiment illustrated in FIG. 5A, each of conductors 80 and 82A-82C iselectrically coupled to a single one of electrodes 74 and 76A-76C,respectively. In this manner, each of electrodes 74 and 76A-76C may beindependently activated. Electrodes 74 and 76A-76C may be coupled to anIMD (e.g., IMD 12 of FIG. 1) using an industry standard-4 (IS-4)connector, which allows the connection of up to four independentlyactivatable channels. More specifically, conductors 80 and 82A-82C maycouple electrodes 74 and 76A-76C to an IMD (e.g., IMD 12 of FIG. 1) viaan IS-4 connector. An IS-4 compatible lead may be easily coupled to anIMD configured according to the IS-4 standard.

The configuration, type, and number of conductors 80 and 82A-82C is notlimited to the embodiment illustrated in FIG. 5A and, in otherembodiments, lead 70 may include any configuration, type, and number ofconductors. As one example, in some embodiments, each of conductors 80and 82A-82C may be coiled conductors. Additionally or alternatively, oneconductor may be electrically coupled to at least two electrodes. Inother embodiments, lead 70 may include a multiplexer such that lead body72 may include fewer conductors than electrodes while allowing each ofthe electrodes to be independently activated.

FIG. 5B is a cross-sectional view of electrode segments 76A-76C alongline 5B in FIG. 5A. As previously described, each of electrode segments76A-76C is separated by insulative material 78. The center of lead 70may include a lumen 84 to accommodate a delivery device such as astylet, guidewire or a hybrid of a stylet and guidewire. A deliverydevice may be used to help position lead 70 at a target location duringimplantation of lead 70. Electrical conductors 82A-82C are coupled toelectrode segments 76A-76C, respectively. Each of conductors 82A-82Cextends from electrodes 76A-76C to a proximal end of lead body 72 tocouple electrodes 76A-76C to an IMD (e.g., IMD 12 of FIG. 1).

As described previously, the separation between electrode segments mayimpact the size of the stimulation field. In the embodiment illustratedin FIG. 5B, electrodes 76A and 76B are separated by arc 86, electrodes76A and 76C are separated by arc 88, and electrodes 76B and 76C areseparated by arc 90. Each of arcs 86, 88, and 90 may extend anywherefrom about 1 degree of arc to about 179 degrees of arc. In theembodiment illustrated in FIG. 5B, arcs 86 and 88 are about the samesize, and arc 90 is greater than each of arcs 86 and 88.

In some embodiments, electrodes 76A-76C may have different surfaceareas. For example, the surface area of the anode electrodes may beequal to or larger than the surface area of the cathode electrode. Forpurposes of example, electrode 76A may be referred to as cathode 76A andelectrodes 76B and 76C may be referred to as anodes 76B and 76C.However, electrodes 76A-76C are not limited to this configuration.

In some embodiments, the ratio of the surface area of cathode 76A to thesurface area of each of anodes 76B and 76C may range from about 1 to 1to about 1 to 7. In some embodiments, the ratio of the surface area ofcathode 76A to the surface area of each of anodes 76B and 76C may beabout 1 to 3. Providing cathode 76A with a smaller surface area than thesurface area of each of anodes 76B and 76C may limit anodal corrosion.Additionally, increasing the surface area of each of anodes 76B and 76Cmay spread the voltage drop out over the surface area of anodes 76B and76C.

In one embodiment, at least a portion of lead 70, such as electrodes 74or a separate marker loaded in or formed on lead body 72, may include aradio-opaque material that is detectable by imaging techniques, such asfluoroscopic imaging or x-ray imaging. For example, as describedpreviously, electrodes 74 and 76A-76C may be made of platinum iridium,which is detectable via imaging techniques. This feature may be helpfulfor maneuvering lead 70 relative to a target site within the body.Radio-opaque markers, as well as other types of markers, such as othertypes of radiographic and/or visible markers, may also be employed toassist a clinician during the introduction and withdrawal of stimulationlead 70 from a patient. Markers identifying the location of eachelectrode may be particularly helpful. Since the electrodes rotate withthe lead body, a clinician may rotate the lead and the electric field tostimulate a desired tissue. Markers may help guide the rotation.

FIG. 6 is a side view of a distal end of an example lead 100. Lead 100is substantially similar to lead 70 of FIGS. 5A and 5B but includes arecessed ring electrode 104. Lead 100 includes a lead body 102 andelectrodes 104 and 106A-106C. Electrodes 106A-106C may be substantiallysimilar to electrodes 76A-76C of lead 70 and may be arranged in asimilar configuration.

Electrode 104 is recessed relative to lead body 102. More particularly,the diameter D2 of electrode 104 is smaller than the diameter D1 of leadbody 102 such that electrode 104 is recessed relative to lead body 102.Recessed electrode 104 may aid in limiting the distance a stimulationfield extends from an outer diameter of lead body 102 in radialdirection 108 perpendicular to the longitudinal axis of lead body 102relative to an electrode having a diameter D2 equal to diameter D1 oflead body 102. The distance a stimulation field extends from an outerdiameter of lead body 102 in radial direction 108 perpendicular to thelongitudinal axis of lead body 102 may also be referred to as the depthof the stimulation field. The recessed electrode 104 draws thestimulation field closer to the longitudinal axis of lead body 102. Inthis manner, the relationship between diameter D2 of electrode 104 andD1 of lead body 102 may aid in controlling the depth of the stimulationfield.

Shield 110 is positioned on an outer surface of recessed ring electrode104 such that shield 110 is substantially flush with lead body 102. Thisallows lead 100 to be isodiametric throughout the length of lead body102, which may be helpful in preventing thrombosis. Allowing lead 100 tobe isodiametric throughout the length of lead body 102 may also makeimplantation of lead 100 easier.

FIG. 7 is a side view of a distal end of an example lead 120. Like lead100, lead 120 is also substantially similar to lead 70 of FIGS. 5A and5B but includes a protruded ring electrode 124. Lead 120 includes a leadbody 122 and electrodes 124 and 126A-126C. Electrodes 126A-126C may besubstantially similar to electrodes 76A-76C of lead 70 and may bearranged in a similar configuration.

Electrode 124 protrudes relative to lead body 122. More particularly,the diameter D4 of electrode 124 is larger than the diameter D3 of leadbody 122 such that electrode 124 protrudes relative to lead body 122.Protruded electrode 124 may aid in increasing the distance a stimulationfield extends from an outer diameter of lead body 122 in radialdirection 128 perpendicular to the longitudinal axis of lead body 122relative to an electrode having a diameter D4 equal to diameter D3 oflead body 122. The protruded electrode 124 extends the stimulation fieldfarther from the longitudinal axis of lead body 122. In this manner, therelationship between diameter D4 of electrode 124 and D3 of lead body122 may aid in controlling the depth of the stimulation field. Astimulation field with increased depth may be useful in deliveringstimulation to a target stimulation site further from lead body 122 thanreachable if the diameter D4 of electrode 124 equaled the diameter D3 oflead body 122.

Recessed and protruded electrodes are described in further detail incommonly-assigned U.S. Utility patent application Ser. No. ______ byEggen et al., entitled, “STIMULATION FIELD MANAGEMENT” (attorney docketnumber P0030110.02/1111-006US01), which was filed on the same date asthe present disclosure and is hereby incorporated by reference.

FIG. 8 is a side view of a distal end of another example lead 130including electrode segments 134A-134B, 136A-136C and 138A-138C at itsdistal end. Lead 130 is substantially similar to lead 70 of FIGS. 5A and5B but includes additional electrode segments 134A-134C and 136A-136Caxially displaced from electrode segments 138A-138C. Lead 130 includes alead body 132 and electrodes 134A-134B, 136A-136C, and 138A-138C.

Electrodes 138A-138C may be substantially similar to electrodes 76A-76Cof lead 70 and may be arranged in a similar configuration. For example,a cross-sectional view of electrodes 138A-138C may be substantiallysimilar to the cross-sectional view of electrode 76A-76C illustrated inFIG. 5B. Additionally, both rows of electrode segments 136A-136C and134A-134C may have cross-sections substantially similar to theembodiment illustrated in FIG. 5B. However, the configuration, number,and type of electrodes illustrated in and described with respect to FIG.8 are merely exemplary. In other embodiments, lead 130 may include anynumber of rows of electrode segments, any number of electrode segmentsper row, and any cross-sectional configuration. Lead 130 may alsoinclude electrode segments positioned at various radial and axialpositions of lead body 132 such that the electrode segments do not formrows.

An IMD (e.g., IMD 12 of FIG. 1) may configure one of electrode segments134A-134C, 136A-136C, and 138A-138C as a cathode and two adjacentelectrode segments as anodes. As one example, IMD 12 may configureelectrode segment 136A as a cathode and electrode segments 136B and 138Aas anodes. Electrode segment 136B (the first anode) is located at aradial position adjacent to electrode segment 136A (the cathode) and thesame axial position as electrode segment 136A (the cathode). Electrodesegment 138A (the second anode) is located at the same radial positionas electrode segment 136A (the cathode) and an axial position adjacentto electrode segment 136A (the cathode). In this manner, the electricalfield may be constrained from extending beyond electrode segments 136Band 138A (the anodes). For example, the electrical field may not extendtransversely outward from the portion of lead body 132 containingelectrode segment 136B. Additionally, the electrical field may notextend past electrode segment 138A such that the most distal point ofthe electrical field may be located at electrode segment 138A. The anodeand cathode configuration may be based on the location of a targettissue site and/or a non-target, potentially undesirable, site.

As another example, IMD 12 may configure electrode segment 136A as acathode and electrode segments 134A and 138A as anodes. Electrodesegments 134A and 138A (the anodes) are located at the same radialposition as electrode segment 136A (the cathode) and axial positionsadjacent to electrode segment 136A (the cathode). In this manner, theelectrical field may be constrained from extending beyond electrodesegments 134A and 138A (the anodes). For example, the electrical fieldmay not extend more distal than electrode segment 138A or more proximalthan electrode segment 134A. Such an anodal shielding configuration maybe used to limit the length of the electrical field along the length oflead body 132.

Other anodal shielding configurations may use at least two electrodesegments at least one radial position of lead 130 and at least one axialposition of lead 130. For example, in some embodiments, three or moreelectrode segments 134, 136, 138 at various axial or radial positionsrelative to a cathode may be activated to substantially surround thecathode, e.g., four more adjacent electrode segments forming a square,diamond, or other geometric shaped “box” around the cathode may beactivated as anodes to constrain the resulting electrical field. Anyanodal shielding configuration including a cathode and at least twoadjacent anodes may be utilized to direct the electrical field toward atarget tissue site and/or away from a non-target, potentiallyundesirable, site.

FIG. 9 is a flowchart illustrating an example technique for evaluatingat least one electrode configuration of an implantable medical lead forLV pacing in a patient. While the description of FIG. 9 primarily refersto lead 130 of FIG. 8, in other examples, the techniques for evaluatingan electrode configuration may be applied to lead 14, 16, 50, 70, 100,120, 150, 240 or another lead. While the technique of FIG. 9 isdescribed with respect to processor 20 of IMD 12, it could be performedby either of processor 20 of IMD 12, processor 40 of programmer 19 orboth processors 20 and 40 could cooperate to perform the technique. Asthis example illustrates, a processor as described herein may includemore than one processor within more than one device.

Processor 20 controls a switch device to apply the stimulation signalsgenerated by stimulation generator 28 to selected electrodes of lead 130with specified polarities (150). The activated electrodes and theirpolarities may be referred to as an electrode configuration. Theelectrode configuration used for stimulation delivery may be stored inmemory 22 of IMD 12 and accessed by processor 20 to control signalgenerator 28 and switching device 29 accordingly. In some embodiments,processor 40 of programmer 19 may send instructions to IMD 12 that causeprocessor 20 to access the stored electrode configuration. In otherembodiments, rather than storing the electrode configuration in memory22 of IMD 12, processor 40 of programmer 19 may send the electrodeconfiguration to IMD 12 along with the instructions. In someembodiments, a computer-readable medium, e.g., memory 22 of IMD 12 ormemory 42 of programmer 19, may store instructions that cause aprocessor, e.g., processor 20 of IMD 12 or processor 40 of programmer19, to perform the functions described with respect to FIG. 9.

To aid in evaluating the electrode configuration, processor 40 ofprogrammer 19 evaluates responses of target tissue and non-target tissueto the stimulation. For example, processor 40 may evaluate capturethresholds, such as both a pacing capture amplitude and a phrenic nervecapture amplitude (152). In some embodiments, the pacing captureamplitude and the phrenic nerve capture amplitude each comprise avoltage amplitude. However, the amplitudes are not limited to voltageamplitudes. For example, at least one of the pacing capture amplitudeand the phrenic nerve capture amplitude may comprise a currentamplitude. Any therapy parameter used in the therapy directed to thetarget tissue. For example, a capture threshold may be a stimulationamplitude, stimulation waveform, stimulation pulse width, stimulationpulse frequency, other therapy parameter or a combination of therapyparameters.

Processor 40 of programmer 19 may evaluate each of the pacing captureamplitude and the phrenic nerve capture amplitude by detecting a minimumamplitude (i.e., threshold amplitude) at which capture occurs ordetermining that capture does not occur at a maximum output. The maximumoutput may correspond to a maximum output, e.g., voltage or current,that may be produced by signal generator 28 of IMD 12.

The processor may detect pacing capture by monitoring signals from atleast one of electrodes 134, 136, 138 (e.g., received via telemetriccommunication with IMD 12 in the case of processor 40 of programmer 19)or sensor 17 and determining whether the signals indicate LV pacingcapture. As one example, sensor 17 may include an oxygen sensor thatdetects the partial pressure of oxygen in the LV of patient 18. Anincreased oxygen level in the LV may indicate increased cardiac outputand LV pacing capture. An oxygen sensor placed in the pulmonary arterymay also generate a signal indicative of cardiac output and,consequentially, LV pacing capture. As another example, processor mayreceive an electrocardiogram (ECG) signal from at least one ofelectrodes 134, 136, 138 or sensor 17 and analyze the ECG signal todetect the occurrence of LV pacing capture. Processor 40 may analyze thetiming and widths of various waves of the ECG signal and/or the presenceof an evoked potential to detect LV pacing capture. As other examples,processor 40 may monitor a heart rate of patient 18 and/or thecontractility of heart 5, e.g., via a signal received from anaccelerometer.

Processor 40 may, additionally or alternatively, receive user feedbackregarding LV pacing capture, e.g., via user interface 44. For example, aclinician may use ultrasound, other imaging techniques, patientfeedback, or other evaluative techniques to monitor LV pacing capture.The clinician may alert processor 40 when LV pacing capture occurs viauser interface 44.

Similarly, processor may detect phrenic nerve capture based on signalsfrom at least one of electrodes 134, 136, 138 or sensor 17 and/or userfeedback received via user interface 44. Since phrenic nerve stimulationmay cause hiccups, an accelerometer may be used to detect hiccups and,consequentially, phrenic nerve stimulation. The accelerator may be anexternal sensor 17 placed on the stomach of patient 18. Alternatively,the accelerator may be implanted within patient 18, e.g., implanted onlead body 132 of lead 130. Movement of lead body 132 may indicatephrenic nerve stimulation. As another example, processor 40 may receivefeedback from a user via user interface 44 indicating the occurrence ofa hiccup.

To evaluate the capture amplitudes, processor 20 of IMD 12 mayiteratively and/or automatically increase a voltage or current amplitudeof the stimulation signal until both pacing and phrenic nerve captureare detected. The amplitude at which capture is first detected may berecorded for both pacing and phrenic nerve capture. If the amplitude ofthe stimulation signal is increased to the maximum output that IMD 12can support without pacing and/or phrenic nerve capture, a no captureindication may be recorded for the pacing and/or phrenic nerveamplitude.

In some embodiments, processor 20 may present the results of the pacingand phrenic nerve capture evaluation to a user, e.g., via user interface44 of programmer 19. The user may select at least one electrodecombinations based on the displayed results.

A suitability index value may optionally be determined for the electrodeconfiguration based on the evaluation of the pacing and phrenic nervecapture amplitudes (154). In some embodiments, the processor maydetermine the suitability index value based on the results of the pacingand phrenic nerve capture amplitude evaluation. In other embodiments,the results may be sent to programmer 19, and processor 40 of programmer19 may determine the suitability index value.

As one example, the suitability index value may be the ratio of thephrenic nerve capture amplitude to the pacing capture amplitude. When aplurality of electrode configurations are evaluated, suitability indexvalues for each of the electrode configurations may be easily compared.The suitability index value may be presented to a user, e.g., via userinterface 44 of programmer 19 in addition to or as an alternative todisplaying the results of the pacing and phrenic nerve captureevaluation.

As mentioned previously, a plurality of electrode configurations may beevaluated. FIG. 10 is a flowchart illustrating an example technique forevaluating a plurality of electrode configurations for LV pacing in apatient. In some embodiments, a computer-readable medium, e.g., memory22 of IMD 12 or memory 42 of programmer 19, may store instructions thatcause a processor, e.g., processor 20 of IMD 12 or processor 40 ofprogrammer 19, to perform the functions described with respect to FIG.9. As previously described with respect to FIG. 9, processor 20 controlsswitch device 29 to apply the stimulation signals generated bystimulation generator 28 to a specific electrode configuration of lead130 (150), and both a pacing capture amplitude and a phrenic nervecapture amplitude are evaluated (152).

If additional electrode configurations are to be tested (160), the nextelectrode configuration is selected (162). For example, a user mayanalyze the results of the pacing and phrenic nerve capture amplitudeevaluation and/or a suitability index value via programmer 19 and chosewhich, if any, electrode configuration to test next. As another example,a list of electrode configuration to test may be predetermined. The listmay include electrode configurations chosen by a clinician and selectingthe next electrode combination may comprise selecting the next electrodeconfiguration on the list until all of the listed combinations have beentested. As yet another embodiment, a processor, e.g., processor 20 ofIMD 12 or processor 40 of programmer 19, may analyze the results of thepacing and phrenic nerve capture amplitude evaluation and/or asuitability index value and chose which, if any, electrode configurationto test next.

If no additional electrode configurations are to be tested (160), atleast one electrode configuration may be selected for LV pacing (164). Auser of programmer 19, processor 20 of IMD 12, and/or processor 40 ofprogrammer 19 may facilitate the selection. As one example, programmer19 displays results of the capture evaluation for each electrodeconfigurations, and a user makes a selection using user interface 44 ofprogrammer 19.

In some embodiments, the selection may be at least partially based onsuitability index values. As described previously, the suitability indexvalue may be the ratio of the phrenic nerve capture amplitude to thepacing capture amplitude. When a plurality of electrode configurationsare evaluated, suitability index values for each of the electrodeconfigurations may be easily compared.

In addition to suitability index values, the selection may be based onthe pacing capture amplitude values. A low pacing capture amplitude maypermit therapy delivery with a low amplitude, which may subsequentlyreduce power consumption and increase battery life. In one exampleprocedure, a processor, e.g., processor 20 of IMD 12 or processor 40 ofprogrammer 19, may first compare the suitability index values to athreshold value and then evaluate the pacing capture amplitude valuesfor a subset of electrode configurations. For example, the processor maycompare each of the suitability index values to a threshold value andeliminate electrode configurations with suitability index values belowthe threshold value from consideration. The threshold value may beclinician-specific and may be entered using user interface 44 ofprogrammer 19. As one example the threshold comparison may specify thatthe phrenic nerve capture amplitude must be at least two times greaterthan the pacing capture amplitude. The electrode configurations withsuitability index values that meet this criterion may be furtherevaluated based on pacing capture amplitude values.

The processes described above with respect FIGS. 9 and 10 mayalternatively be applied to evaluating at least one electrodeconfiguration of an implantable medical lead for vagus nervestimulation. Instead of evaluating pacing capture and phrenic nervecapture amplitudes as described with respect to LV pacing, vagus nervecapture and muscle capture amplitudes may be evaluated. As describedpreviously, it may be desirable to selectively stimulate the vagus nervewithout stimulating the muscle tissue proximate to the vagus nerve.Stimulation of the muscle tissue of the neck may cause undesirablemuscle contraction. An example suitability index value for vagus nervestimulation may be the ratio of the muscle capture amplitude to thevagus nerve capture amplitude.

Like LV pacing and phrenic nerve capture, each of vagus nerve captureand neck muscle capture may be detected based on signals from at leastone of electrodes 134, 136, 138 or sensor 17 and/or user feedbackreceived via user interface 44. As one example, an accelerometerimplanted within or external to the neck of patient 18 may detectcontraction of the neck muscles caused by capture of those muscles. Asanother example, a user may provide feedback indicating the occurrenceof neck muscle contraction via user interface 44. Vagus nerve capture,for example, may be detected based on the heart rate of patient 18,since stimulation of the vagus nerve may cause a decrease in heart rate.

FIG. 11 is a side view of an embodiment of a distal end of a lead 240,which may, for example, correspond to either of leads 14, 16 of FIG. 1.Lead 240 includes four electrodes 244A-244D (collectively “electrodes244”). Lead 240 includes a lead body 242 that extends from a proximalend (not shown) to a distal end that includes electrodes 244. Lead 240may coupled to an IMD (e.g., IMD 12 of FIG. 1) or other device includinga stimulation generator. Lead body 242 may be sized to fit in a smalland/or large coronary vein. Accordingly, electrodes 244 may also besized based on the size of lead body 242 and a target stimulation sitewithin a patient (e.g., patient 18 of FIG. 1).

In some embodiments, at least one of electrodes 244 may be ringelectrodes, each with a substantially circular cross-section. In otherembodiments, electrodes 244 may comprise segmented or partial ringelectrodes. In the embodiment illustrated in FIG. 11, electrodes 244 maybe coupled to a device including a stimulation generator using an IS-4connector, which allows the connection of up to four independentlyactivatable channels. More specifically, conductors (not shown) maycouple electrodes 244 to a device including a stimulation generator viaan IS-4 connector. In other embodiments, lead 240 may include anyconfiguration, type, and number of electrodes 244 and is not limited tothe embodiment illustrated in FIG. 11.

In the embodiment illustrated in FIG. 11, electrodes 244 are axiallydisplaced from one another along the length of lead body 242.Additionally, electrodes 244 are arranged in two pairs of closely spacedelectrodes. For example, electrodes 244A and 244B comprise a first pair246A, and electrodes 244C and 244D comprise a second pair 246B.Additionally, lead 240 may also include monolithic controlled releasedevice (MCRD) 247A containing a steroid between electrodes 244A and 244Bof pair 246A and MCRD 247B containing a steroid between electrodes 244Cand 244D of pair 246B. One of electrodes 244 in one of pairs 246 may beconfigured as a cathode and the other electrode of the same pair may beconfigured as an anode. This configuration may be referred to as abipolar mode. The other pair 246 may be activated in a similar manner.The two pairs 246 of electrodes 244 may allow an IMD (e.g., IMD 12 ofFIG. 1) to deliver a stimulation signal to two different sitescorresponding to the locations of pairs 246. Pairs 246 may be activatedindividually and/or simultaneously. For example, a clinician may beallowed to switch between pairs 246 (e.g., via programmer 19 of FIG. 1)if one of pairs 246 is or becomes less optimal.

The distance D5 between electrodes 244A and 244B of pair 246A may belimited to help control the size of the stimulation field. The distanceD6 between electrodes 244C and 244D of pair 246B may also be limited ina similar manner. Limiting distances D5 and D6 may provide a voltagedrop to the anode and reduce the size of the electrical field comparedto a lead with larger spacing between the cathode and anode.

The short cathode to anode spacing D5 and D6 may be useful in preventingundesirable stimulation of nerves and/or muscles outside the proximityof lead body 242. As one example, a field of limited size may beparticularly useful in LV pacing applications. The short cathode toanode spacing D5 and D6 may allow placement of a LV lead to be performedwith minimal chance of stimulating the phrenic nerve. Since theelectrical field created using a closely spaced cathode and anode in abipolar mode is limited in size, the electrical field may be preventedfrom reaching the phrenic nerve. Providing two pairs 46 of electrodes 44may allow dual stimulation of two stimulation sites while avoidingphrenic nerve stimulation.

A stimulation field limited in size may also be useful for otherapplications. As one example, a limited electrical field may be usefulin stimulation of the vagus nerve. Stimulation of the vagus nerve may beperformed to decrease heart rate. The vagus nerve is positionedproximate to muscles of the neck, which may inadvertently be stimulatedalong with the vagus nerve. Controlling the depth of the stimulationfield may aid in preventing stimulation of the neck muscles. As anotherexample, an electrical field of limited size may be useful in atrialstimulation where it may be desirable to avoid stimulating specificischemic tissue regions. In general, close anode to cathode spacing maybe beneficial in any application where controlling the reach of thestimulation field is desirable.

As one example, when electrode 244D is configured as a cathode andelectrode 244C is configured as an anode, outline 226 may represent theouter boundaries of the stimulation field. In contrast, using the sameanode and cathode configuration but increasing the distance D6 betweenelectrodes 244C and 244D would generally increase the size of thestimulation field along the longitudinal axis of lead body 242 indirection 228 and increase the depth of the stimulation field indirection 229 perpendicular to the longitudinal axis of lead body 242.The close anode to cathode spacing D6 may limit the length of thestimulation field along the longitudinal axis of lead body 242 and/orthe depth of the stimulation field perpendicular to the longitudinalaxis of lead body 242. In this manner, the anode to cathode spacing D6may be selected to aid in selectively exciting a tissue based on thegeometrical proximity to lead 240 and/or the field gradient to which thetissue responds.

Each of distances D5 and D6 may be less than about 10 mm. For example,in some embodiments, the cathode to anode spacing D5 and D6 may bebetween about 0.254 mm and about 6.35 mm. Further, in some embodiments,the cathode to anode spacing D5 and D6 may be about 1 mm.

In some embodiments, the surface area of the anode electrode may beequal to or larger than the surface area of the cathode electrode. Forpurposes of example, electrode 44B may be referred to as cathode 244Band electrode 244A may be referred to as anode 244A. However, electrodes244A and 244B are not limited to this configuration. For example, theposition of the cathode and anode within electrode pair 246A may beswitched. Additionally, electrodes 244C and 244D of electrode pair 246Bmay have a similar configuration to that of electrode pair 246A.

In some embodiments, the ratio of the surface area of cathode 244B tothe surface area of anode 244A may range from about 1 to 1 to about 1 to7. In some embodiments, the ratio of the surface area of cathode 244B tothe surface area of anode 44A may be about 1 to 3. As one example, thesurface area of cathode 244B may be about 2 mm², and the surface area ofanode 44A may be about 6 mm². In another embodiment, the surface area ofcathode 244B may be about 5 mm², and the surface area of anode 44A maybe about 15 mm². Providing cathode 244B with a smaller surface area thanthe surface area of anode 244A may limit anodal corrosion. Additionally,increasing the surface area of anode 244A spreads the voltage drop outover the surface area of anode 244A.

Lead 240 may be used as part of a medical system that provides automatedevaluation of a plurality of lead electrode configurations. For example,different electrode configurations using lead 240 include not onlybipolar configurations using one of electrode pairs 246B configured toinclude an anode and a cathode, but also using a different combinationof electrodes 244 as anodes and/or cathodes and even using any ofelectrodes 244 as unipolar electrodes.

The spacing and number of ring electrodes in lead 240 is merelyexemplary. Leads having any number of ring electrodes at different axialpositions of lead may be used as part of a medical system that providesautomated evaluation of a plurality of lead electrode configurations.

Various embodiments have been described. However, modifications may bemade to the described embodiments within the spirit of the presentdisclosure. For example, leads used in conjunction with the techniquesdescribed herein may include fixation mechanisms, such as tines thatpassively secure a lead in an implanted position or a helix located at adistal end of the lead that requires rotation of the lead duringimplantation to secure the helix to a body tissue.

As another example, although described herein as being coupled to IMDs,implantable medical leads of according to the present disclosure mayalso be percutaneously coupled to an external medical device for deliverof electrical stimulation to target locations within the patient.

These and other embodiments are within the scope of the followingclaims.

1. A medical system comprising: a plurality of electrodes; at least onesensor configured to output at least one signal based on at least onephysiological parameter of a patient; and a processor configured to:control delivery of stimulation to the patient using a plurality ofelectrode configurations, wherein each of the electrode configurationscomprises at least one of the plurality of electrodes, for each of theelectrode configurations, determine a first response of target tissue tothe stimulation based on the signals, and a second response ofnon-target tissue to the stimulation based on the signals, and select atleast one of the electrode configurations for delivery of stimulation tothe patient based on the first and second responses for the electrodeconfigurations.
 2. The medical system of claim 1, further comprising atleast one implantable medical lead, wherein the at least one implantablemedical lead includes the plurality of electrodes.
 3. The medical systemof claim 2, wherein the at least one implantable medical lead comprisescardiac pacing leads, wherein the target tissue comprises tissue of theleft ventricle of the patient and the non-target tissue comprises tissueof the phrenic nerve of the patient.
 4. The medical system of claim 2,wherein the target tissue comprises tissue of the vagus nerve of thepatient and the non-target tissue comprises muscle tissue of the patientadjacent to the vagus nerve.
 5. The medical system of claim 2, furthercomprising an implantable medical device including a stimulationgenerator coupled to the implantable medical leads, wherein theprocessor controls the implantable medical device to deliver thestimulation to the patient using the plurality of electrodeconfigurations.
 6. The medical system of claim 1, wherein the at leastone sensor includes: a first sensor that outputs a first signal based ona first physiological parameter of the patient that indicates the firstresponse of the target tissue; and a second sensor that outputs a secondsignal based on a second physiological parameter of the patient thatindicates the second response of the non-target tissue.
 7. The medicalsystem of claim 1, wherein the physiological parameters of the patientare selected from a group consisting of: an electrocardiogram (ECG);heart rate; QRS width; atrioventricular (AV) dissociation; respirationrate; respiratory volume; core temperature; diaphragmatic stimulation;skeletal muscle activity; blood oxygen level; cardiac output; bloodpressure; intercardiac pressure; time derivative of intercardiacpressure (dP/dt); electromyogram (EMG) parameters; and anelectroencephalogram (EEG) parameters.
 8. The medical system of claim 1,wherein the first response of target tissue comprises a first capturethreshold of target tissue and the second response of non-target tissuecomprises a second capture threshold of non-target tissue.
 9. Themedical system of claim 8, wherein the first and second capturethresholds are selected from a group consisting of: a stimulationwaveform; a stimulation amplitude; a stimulation pulse width; and astimulation pulse frequency.
 10. The medical system of claim 8, whereindetermining the first and second responses for the electrodeconfigurations includes determining that at least one of the first andsecond capture thresholds exceeds a maximum stimulation amplitudeallowed by the medical system.
 11. The medical system of claim 1,wherein selecting at least one of the electrode configurations fordelivery of stimulation to the patient based on the first and secondresponses for the electrode configurations includes determining a valueof a suitability index for each of the electrode configurations based ona ratio of the first second capture threshold to the second capturethreshold for each of the electrode configurations.
 12. The medicalsystem of claim 1, wherein selecting at least one of the electrodeconfigurations for delivery of stimulation to the patient based on thefirst and second responses for the electrode configurations comprises:automatically selecting at least one electrode configuration of theplurality of electrode configurations; and controlling delivery ofstimulation to the patient using the at least one electrodeconfiguration.
 13. The medical system of claim 1, further comprising auser interface, wherein selecting at least one of the electrodeconfigurations for delivery of stimulation to the patient based on thefirst and second responses for the electrode configurations includes:presenting the first and second responses to a clinician via the userinterface; and receiving an input from the clinician via the userinterface selecting at least one of the electrode configurations fordelivery of stimulation to the patient.
 14. The medical system of claim13, wherein the first response of target tissue comprises a firstcapture threshold of target tissue and the second response of non-targettissue comprises a second capture threshold of non-target tissue. 15.The medical system of claim 1, further comprising a clinician programmerincluding the processor.
 16. The medical system of claim 1, wherein theselected at least one of the electrode configurations for delivery ofstimulation to the patient based on the first and second responses forthe electrode configurations include an electrode configurationcomprising: a first electrode segment configured as a first anode; asecond electrode segment configured as a cathode; and a third electrodesegment configured as a second anode, wherein the third electrodesegment being opposite the first electrode segment relative to thesecond electrode segment.
 17. The medical system of claim 1, whereinselecting at least one of the electrode configurations for delivery ofstimulation to the patient based on the first and second responses forthe electrode configurations comprises selecting at least one electrodeconfiguration of the plurality of electrode configurations to optimizethe physiological parameters of the patient.
 18. A method for evaluatingtherapeutic stimulation of a plurality of electrode configurationscomprising: controlling delivery of stimulation to a patient using theplurality of electrode configurations; for each of the electrodeconfigurations, determining a first response of target tissue to thestimulation and a second response of non-target tissue to thestimulation based on at least one sensor signal, wherein the sensorsignals are based on at least one physiological parameter of thepatient; and selecting at least one of the electrode configurations fordelivery of stimulation to the patient based on the first and secondresponses for the electrode configurations.
 19. The method of claim 18,wherein the plurality of electrode configurations include sets of atleast one electrode included on at least one implantable medical lead.20. The method of claim 19, wherein the at least one implantable medicallead are cardiac pacing leads, wherein the target tissue comprises theleft ventricle of the patient and the non-target tissue comprises thephrenic nerve of the patient.
 21. The method of claim 19, wherein thetarget tissue comprises the vagus nerve of the patient and thenon-target tissue comprises a muscle of the patient adjacent to thevagus nerve.
 22. The method of claim 19, further comprising controllinga stimulation generator coupled to the implantable medical leads todeliver the stimulation to the patient using the plurality of electrodeconfigurations.
 23. The method of claim 18, wherein the sensor signalsare sent by at least one sensor including: a first sensor that outputs afirst signal based on a first physiological parameter of the patientthat indicates capture of the target tissue; and a second sensor thatoutputs a second signal based on a second physiological parameter of thepatient that indicates capture of the non-target tissue.
 24. The methodof claim 18, wherein the physiological parameters of the patient areselected from a group consisting of: an electrocardiogram (ECG); heartrate; QRS width; atrioventricular (AV) dissociation; respiration rate;respiratory volume; core temperature; diaphragmatic stimulation;skeletal muscle activity; blood oxygen level; cardiac output; bloodpressure; intercardiac pressure; time derivative of intercardiacpressure (dP/dt); electromyogram (EMG) parameters; and anelectroencephalogram (EEG) parameters.
 25. The method of claim 18,wherein the first and second responses are selected from a groupconsisting of: a stimulation waveform; a stimulation amplitude; astimulation pulse width; and a stimulation pulse frequency.
 26. Themethod of claim 18, wherein the first response comprises a first capturethreshold and the second response comprises a second capture threshold,wherein determining the first and second responses for the electrodeconfigurations includes determining that at least one of the first andsecond capture thresholds exceeds a maximum stimulation amplitudeallowed by the method.
 27. The method of claim 18, wherein the firstresponse comprises a first capture threshold and the second responsecomprises a second capture threshold, wherein selecting at least one ofthe electrode configurations for delivery of stimulation to the patientbased on the first and second responses for the electrode configurationsincludes determining a value of a suitability index for each of theelectrode configurations based on a ratio of the first second capturethreshold to the second capture threshold for each of the electrodeconfigurations.
 28. The method of claim 18, wherein selecting at leastone of the electrode configurations for delivery of stimulation to thepatient based on the first and second responses for the electrodeconfigurations comprises: automatically selecting at least onepreferable electrode configuration of the plurality of electrodeconfigurations; and controlling delivery of stimulation to the patientusing the at least one preferable electrode configuration.
 29. Themethod of claim 18, wherein selecting at least one of the electrodeconfigurations for delivery of stimulation to the patient based on thefirst and second responses for the electrode configurations includes:presenting the first and second responses to a clinician via a userinterface; and receiving an input from the clinician via the userinterface selecting at least one of the electrode configurations fordelivery of stimulation to the patient.
 30. The method of claim 18,wherein the selected at least one of the electrode configurations fordelivery of stimulation to the patient based on the first and secondresponses for the electrode configurations include an electrodeconfiguration comprising: a first electrode segment configured as afirst anode; a second electrode segment configured as a cathode; and athird electrode segment configured as a second anode, wherein the thirdelectrode segment being opposite the first electrode segment relative tothe second electrode segment.
 31. The method of claim 18, whereinselecting at least one of the electrode configurations for delivery ofstimulation to the patient based on the first and second responses forthe electrode configurations comprises selecting at least one electrodeconfiguration of the plurality of electrode configurations to optimizethe physiological parameters of the patient.
 32. A computer-readablemedium comprising instructions that cause a programmable processor to:control delivery of stimulation to a patient using a plurality ofelectrode configurations; for each of the electrode configurations,determine a first response of target tissue to the stimulation and asecond response of non-target tissue to the stimulation based on atleast one sensor signal, wherein the sensor signals are based on atleast one physiological parameter of the patient; and select at leastone of the electrode configurations for delivery of stimulation to thepatient based on the first and second responses for the electrodeconfigurations.
 33. The computer-readable medium of claim 32, whereinthe plurality of electrode configurations include sets of at least oneelectrode included on at least one implantable medical lead.
 34. Thecomputer-readable medium of claim 33, wherein the at least oneimplantable medical lead are cardiac pacing leads, wherein the targettissue comprises the left ventricle of the patient and the non-targettissue comprises the phrenic nerve of the patient.
 35. Thecomputer-readable medium of claim 33, wherein the target tissuecomprises the vagus nerve of the patient and the non-target tissuecomprises a muscle of the patient adjacent to the vagus nerve.
 36. Thecomputer-readable medium of claim 33, comprising further instructionsthat cause the programmable processor to control a stimulation generatorcoupled to the implantable medical leads to deliver the stimulation tothe patient using the plurality of electrode configurations.
 37. Thecomputer-readable medium of claim 32, wherein the sensor signals aresent by at least one sensor including: a first sensor that outputs afirst signal based on a first physiological parameter of the patientthat indicates capture of the target tissue; and a second sensor thatoutputs a second signal based on a second physiological parameter of thepatient that indicates capture of the non-target tissue.
 38. Thecomputer-readable medium of claim 32, wherein the physiologicalparameters of the patient are selected from a group consisting of: anelectrocardiogram (ECG); heart rate; QRS width; atrioventricular (AV)dissociation; respiration rate; respiratory volume; core temperature;diaphragmatic stimulation; skeletal muscle activity; blood oxygen level;cardiac output; blood pressure; intercardiac pressure; time derivativeof intercardiac pressure (dP/dt); electromyogram (EMG) parameters; andan electroencephalogram (EEG) parameters.
 39. The computer-readablemedium of claim 32, wherein the first and second capture thresholds areselected from a group consisting of: a stimulation waveform; astimulation amplitude; a stimulation pulse width; and a stimulationpulse frequency.
 40. The computer-readable medium of claim 32, whereinthe first response comprises a first capture threshold and the secondresponse comprises a second capture threshold, wherein determining thefirst and second responses for the electrode configurations includesdetermining that at least one of the first and second capture thresholdsexceeds a maximum stimulation amplitude allowed by the computer-readablemedium.
 41. The computer-readable medium of claim 32, wherein the firstresponse comprises a first capture threshold and the second responsecomprises a second capture threshold, wherein selecting at least one ofthe electrode configurations for delivery of stimulation to the patientbased on the first and second capture responses for the electrodeconfigurations includes determining a value of a suitability index foreach of the electrode configurations based on a ratio of the firstsecond capture threshold to the second capture threshold for each of theelectrode configurations.
 42. The computer-readable medium of claim 32,wherein selecting at least one of the electrode configurations fordelivery of stimulation to the patient based on the first and secondresponses for the electrode configurations comprises: automaticallyselecting at least one preferable electrode configuration of theplurality of electrode configurations; and controlling delivery ofstimulation to the patient using the at least one preferable electrodeconfiguration.
 43. The computer-readable medium of claim 32, whereinselecting at least one of the electrode configurations for delivery ofstimulation to the patient based on the first and second responses forthe electrode configurations includes: presenting the first and secondresponses to a clinician via a user interface; and receiving an inputfrom the clinician via the user interface selecting at least one of theelectrode configurations for delivery of stimulation to the patient. 44.The computer-readable medium of claim 32, wherein the selected at leastone of the electrode configurations for delivery of stimulation to thepatient based on the first and second responses for the electrodeconfigurations include an electrode configuration comprising: a firstelectrode segment configured as a first anode; a second electrodesegment configured as a cathode; and a third electrode segmentconfigured as a second anode, wherein the third electrode segment beingopposite the first electrode segment relative to the second electrodesegment.
 45. The computer-readable medium of claim 32, wherein selectingat least one of the electrode configurations for delivery of stimulationto the patient based on the first and second responses for the electrodeconfigurations comprises selecting at least one electrode configurationof the plurality of electrode configurations to optimize thephysiological parameters of the patient.
 46. A medical devicecomprising: a means for delivering stimulation therapy to a patientusing a plurality of electrode configurations; and a means forevaluating the relative suitability of the of the electrodeconfigurations for delivering stimulation therapy to target tissue ofthe patient.